This study has established a cohort of 200 patients with inflammatory arthritis of less than one year's duration in an attempt to better understand pathogenetic mechanisms involved in early synovitis and to determine prognostic factors associated with the clinical disease course. Synovial biopsies and synovial fluid have been obtained to search for microbial agents and other initiating and modulating factors that may be most readily distinguished early in the disease and to determine the stage of disease at which certain immunologic and hormonal changes become evident. Specimens are evaluated by polymerase chain reaction, in situ hybridization and immuno-electron microscopy for the presence of infectious agents such as difficult to culture chlamydia and to assess cell populations and cytokine profiles present within the synovial membrane. The study will also search for genetic, in particular HLA DR loci, and other features that may be associated with specific forms of inflammatory arthropathies that might predict the subsequent clinical disease course or response to different agents used in treatment of rheumatoid arthritis and other types of chronic inflammatory arthropathies. To date, chlamydia trachomatis DNA, RNA and antigens have been found in approximately 50% of patients with reactive arthritis and in much smaller percentages of patients with rheumatoid arthritis and other forms of arthritis. These studies will contribute to knowledge about the pathogenic events in early arthritis, clarify the role of suspected infectious triggers of synovial inflammation, identify prognostic markers of the clinical course of arthritis and have the potential to assist in the development of new approaches to patient management.